This book offers a theory of language which departs from both structuralist and Chomskyan transformational linguistics in using semantic structure as its base. The theory is illustrated mostly from English by means of a step-by-step analysis of a large part of English semantic structure. A specific and detailed theory of language is thus elaborated, in which the well-formedness of sentences is established at the semantic level, with "postsemantic" processes then responsible for the conversion of semantic into surface structures. Application of the theory is also made to Onondaga, an Iroquois language, showing that the differences between this language and English are relatively trivial in the semantic area but extensive in the area of postsemantic processes. (Author/FWB)